Two different platform conditions exist for passenger ingress and egress onto and from a transit vehicle. The first condition relates to passenger ingress and egress from and onto a ground level or a stationary platform with a horizontal surface of under 14 inches in height above ground level This condition is hereinafter referred to as a low platform. The second condition relates to the passenger ingress and egress from and onto a stationary platform having a horizontal surface which is greater than 14 inches in height above ground level and is typically level with the floor of the transit vehicle. This condition is hereinafter referred to as a high platform.
One approach to accommodate varying platform types is to incorporate a passenger ingress and egress system including a stationary stairwell disposed within a floor surface in combination with a stairwell platform pivotally connected to one side of an upper horizontal plane of the stairwell and manually displaceable to lie in the horizontal plane over the stairwell for accommodating high platforms. The main disadvantage of the stairwell platform is that it does not meet Federal Regulation regarding Americans with Disabilities Act, hereinafter referred to as ADA regulations that the horizontal displacement, generally referred to as the gap, between the high platform edge and stairwell platform of the transit vehicle, with its doors open, can not exceed 3 inches. Due to the gap (or clearance) between the edge of the platform and the outer surface of the transit vehicle being approximately between 2 inches and 3 inches, the outer wall of the transit vehicle being between 2 inches and 3 inches in width, the door construction typically between 1 inch and 2 inches in width, the outer edge of the stairwell platform is approximately between 5 inches and 8 inches away from the edge of the high platform with the doors of a sliding type in a fully open position.
A well-known approach overcoming the gap between the stairwell platform and high platforms is to employ a movable threshold mechanically coupled with the door having a recess or containing multiple door sections, which extends into the cavity occupied by the door thus minimizing the gap.
U.S. Pat. No. 5,070,794 describes a railway vehicle door comprising bottom and top door members, sliding with respect to each other, and connected by locking means. The lower door member is for covering the stairwell opening for passenger loading from a high platform. The door is mounted so as to slide between a closed position and an open position. A stairwell platform is fixed so as to be articulated on an axis substantially perpendicular to the door and is situated substantially in the horizontal plane of the top of the steps, such platform being able to be moved from a vertical position and a position of use in which it is situated in the horizontal plane. A threshold member projects with respect to the external face of the door in order to fill in at least part of the space lying between the edge of the stairwell platform, in the position of use, and the edge of the railway platform. This threshold member is an integral part of the bottom member.
Another approach described in U.S. Pat. No. 6,401,629 utilizes a door having a single member and a threshold at least partially disposed within a recess formed in the door. The vehicle body comprises means for supporting the end of the threshold, which are disposed close to the edge of the door opening opposite to the direction of opening of the door, when the door is open. The means for supporting the end of the threshold element comprise, for example, rollers carried by the end of the threshold and abutment surfaces receiving the rollers fixed to the vehicle body.
The guide means between the threshold member and the door include a rail fixed to the threshold extending in the longitudinal direction of the threshold and projecting from the end of this threshold in the direction of opening of the door, and a slide on which the rail slides, the slide being fixed to the body and having a length at least equal to the length of the threshold.
In the first aspect, the main disadvantage of the prior art system is the complexity of door and threshold construction and protrusion of the threshold beyond the outer wall of the transit vehicle during movement.
In the second aspect, the stairwell platform, when not in use for high platform ingress and egress, is disposed in the first position vertically above the stairwell occupying an additional space and being exposed to the riding passengers.
In the third aspect, this type of gap reduction approach can be only utilized with a single sliding type door, which relies on the adjacent end of the car structure opening to support the threshold. It is well known in the art that a bi-parting type sliding door system can be employed within a door opening of a transit vehicle, requiring both doors to open simultaneously in opposite directions with no support structure available in the center of such opening.
Even though a sliding type door system, particularly of a pocket configuration, is used predominantly in transit service, a plug type door system disposed flush with the outer surface of the transit vehicle and moving first outwardly and then linearly in relationship to such outer surface can be employed in either a single or bi-parting configurations. Such plug type door system, preferable for its esthetics and environment sealing capabilities as well as preferable for elimination of the interior wall of the transit vehicle cannot be utilized with the stationary stairwell platform and a threshold as described above.
Additionally a sliding type door, linearly movable substantially along the outer surface, can be further employed in a transit vehicle for elimination of its interior wall.
As it can be seen from the above discussion there is a need to provide a cost effective approach for accommodating high and low platform boarding which is particularly configured to interface with a biparting door system configuration either of a sliding or plug door type.
ADA regulations further mandate that a vertical displacement between high platform and floor section preferably does not exceed 0.5 inches with the first 0.25 inches disposed in a vertical plane and with the second 0.25 inches disposed at 45 degree angle. Additional vertical displacement exceeding 0.5 inches must be angularly disposed within 1:6 slope, or about 10.5 degrees to enable ingress and egress of passengers with disabilities and, particularly, those passengers with disability using a wheelchair.
Considerations must be also given to prevent any potential interference between a moving stairwell platform and a passenger(s) occupying the stairwell at the time of such movement. This situation is accentuated when applied to unattended stairwell platform operation.